Extraction and Separation of Lanthanum and Actinium by Non-Saponification P507 System

Abstract

Due to the ineffective separation and removal of actinium during the production process of rare earths, the radioactive of some products in China exceed the exemption values(the total activity of α and β less than 1 Bq/g). Using non-saponified 2-ethylhexyl phosphate mono-2-ethylhexyl ester(P507) as an extractant, diethylenetriamine-N, N, N', N'', N''-pentaacetic acid(DTPA) or N-(2-hydroxyethyl)ethylenediamine-N, N', N'-triacetic acid(HEDTA) as aqueous masking agent, lactic acid as acidity buffer, the extraction and separation of lanthanum-actinium elements was studied respectively in hydrochloric acid and nitric acid media in this work. The results show that the weak acid can effectively buffer the acidity of the aqueous phase and promote the coordination reaction to form organic chelates favorably. The extraction properties of La3+ in the above system is better than in the single saponified P507 system. When pH is 3.0 and the initial La3+ concentration is 0.2 mol/L in hydrochloric acid solution, D(La) can reach 5.0 and SF(La/Ac) value is 3-4. Compared with that，SF(La/Ac) can increase to 5-7 in nitric acid system under the fixed conditions of pH as 2.0-2.5, the DTPA/HEDTA and lactic acid concentrations as 0.02 mol/L and 1.0 mol/L, respectively. In this case, Ac3+ is effectively masked and the maximum D(Ac) is only 0.46. Furthermore, the non-saponification P507 system can also preferentially remove the radioactive Ac3+ from the acidic rare earth wastewater, and SF(Ac/La) value can reach 14 with the increase of lactic acid concentration. The phenomenon can be used to achieve the goal of effective control of radioactive substances in the wastewater of rare earth industry.

Keywords

• lanthanum-actinium
• extraction and separation
• non-saponification system
• p507
• rare earth production